The present invention relates to a swivel joint and, more particularly, to a swivel joint having stepped bearing races.
Swivel joints are used to connect fluid pipes in oilfields and in other applications. Swivel joints are generally comprised of interfitting male and female members rotatably connected by a bearing assembly. Typically, inner and outer grooves are incorporated in the male and female members to form a bearing race, and a plurality of ball bearings are housed within the race. Higher demand for compatibility with increased service pressure, wider operating temperature range, and a greater variety of corrosive chemicals has resulted in swivel joint designs with multiple bearing races rather than one bearing race. Even with multiple bearing races high pressures can sometimes cause deformation or brinelling of the bearing races. Such brinelling relaxes the compression of the seal between the male and female members and causes the seal to leak, preventing the swivel joint from swiveling smoothly under pressure and reducing the bearing race life significantly. In addition, erosive wear in the male member under the bearing race can quickly reduce the integrity of the swivel joint.
The present invention provides a swivel joint having two or more bearing races situated in a stepped relationship wherein each bearing race is positioned coaxially with respect to and has an incrementally greater radius than the next adjacent bearing race closer to the end of the male member which engages the female member. The radius of each bearing race is preferably determined as a function of the radius of the ball bearings and the cross sectional areas of the male and female members at the bearing race. In a preferred embodiment of the invention, the radius of each race is determined such that the number of balls in each race is one more than the number of balls in the adjacent race closer the end of the male member which engages the female member.
The present invention improves sealing under extreme conditions and specifically eliminates bearing race brinelling at pressures much greater than is attained with conventional or known swivel joints with minimal increase in weight and cost. This stepped configuration more equally distributes hydrostatic end loading to each bearing race section, enabling maximum total end loading while minimizing load concentration on a particular bearing race. In addition, the stepped configuration permits the male member to have a relatively larger cross section under the bearing race without increasing the overall diameter of the swivel joint, which enables the male member to withstand a relatively greater amount erosive wear and thereby improves the overall integrity of the swivel joint.